Recently, the long term evolution (LTE) project and Worldwide Interoperability Microwave Access (Wimax) and the like in the 4th generation wireless mobile communication system (4G) have been developed rapidly. Application of MIMO has become a milestone of the development of the wireless communication system, and has significantly improved the throughput, the spectrum effectiveness and system link performance of the wireless mobile communication system.
In the current mainstream standards, the most important problem in the multi-antenna technology is the channel information feedback technique. Generally speaking, the channel between the transmitting and receiving antennae can be represented in the form of matrix, and further, the channel matrix can be described and fed back through information of vectors and eigenvalues. The vector information is very important to the precoding technology of MIMO, since it directly affects the performance of the MIMO system. The vectors are generally fed back in a codebook-based feedback method.
The basic principle of codebook based quantitative feedback of channel information is as follows: if it is assumed that the limited feedback channel capacity is B bps/Hz, then the number of available codewords is N=2B. The vector space of the channel matrix constitutes a codebook space ={F1, F2L FN} after quantification. The transmitting end and the receiving end collectively store or generate this codebook in real time (the transmitting end and the receiving end are the same). For each channel implementation H, the receiving end selects a codeword {circumflex over (F)} mostly matched with the channel from  according to certain rules, and feeds back the sequence number i of the codeword to the transmitting end. The transmitting end finds out the pre-coding codeword {circumflex over (F)} according to this sequence number i, and obtains channel information, which is mainly the vector information of the channel.
Generally, the codebook space  may be further divided into codebooks corresponding to multiple Ranks, and each Rank corresponds to multiple codewords to quantify the pre-coding matrix composed of non-zero channel vectors under this Rank. Generally, there will be N columns of codewords when the Rank is N. Therefore, we can divide the codebook  into multiple sub-codebooks according to the Rank, as shown in the following Table 1.
TABLE 1Dividing the codebook    into multiple sub-codebooks according to the Rank Number of layers ν (Rank)12. . .N  . . . The codewordThe codewordThe codewordvector withmatrix withmatrix withthe columnthe columnthe columnnumber of 1number of 2number of N
Wherein, when Rank>1, the codewords needing to be stored are all in the form of matrix, for example this feedback method of codebook quantification is used in the LTE protocol, and the corresponding codebook is as shown in Table 2.
TABLE 2LTE 4Tx codebookCodebookTotal number of layers νindexun12340u0 = [1 −1 −1 −1]TW0{1}W0{14}/{square root over (2)}W0{124}/{square root over (3)}W0{1234}/21u1 = [1 −j 1 j]TW1{1}W1{12}/{square root over (2)}W1{123}/{square root over (3)}W1{1234}/22u2 = [1 1 −1 1]TW2{1}W2{12}/{square root over (2)}W2{123}/{square root over (3)}W2{3214}/23u3 = [1 j 1 −j]TW3{1}W3{12}/{square root over (2)}W3{123}/{square root over (3)}W3{3214}/24u4 = [1 (−1 − j)/{square root over (2)} −j (1 − j)/{square root over (2)}]TW4{1}W4{14}/{square root over (2)}W4{124}/{square root over (3)}W4{1234}/25u5 = [1 (1 − j)/{square root over (2)} j (−1 − j/{square root over (2)}]TW5{1}W5{14}/{square root over (2)}W5{124}/{square root over (3)}W5{1234}/26u6 = [1 (1 + j)/{square root over (2)} −j (−1 + j)/{square root over (2)}]TW6{1}W6{13}/{square root over (2)}W6{134}/{square root over (3)}W6{1324}/27u7 = [1 (−1 + j)/{square root over (2)} j (1 + j)/{square root over (2)}]TW7{1}W7{13}/{square root over (2)}W7{134}/{square root over (3)}W7{1324}/28u8 = [1 −1 1 1]TW8{1}W8{12}/{square root over (2)}W8{124}/{square root over (3)}W8{1234}/29u9 = [1 −j −1 −j]TW9{1}W9{14}/{square root over (2)}W9{134}/{square root over (3)}W9{1234}/210u10 = [1 1 1 −1]TW10{1}W10{13}/{square root over (2)}W10{123}/{square root over (3)}W10{1324}/211u11 = [1 j −1 j]TW11{1}W11{13}/{square root over (2)}W11{134}/{square root over (3)}W11{1324}/212u12 = [1 −1 −1 1]TW12{1}W12{12}/{square root over (2)}W12{123}/{square root over (3)}W12{1234}/213u13 = [1 −1 1 −1]TW13{1}W13{13}/{square root over (2)}W13{123}/{square root over (3)}W13{1324}/2
In the Third party project partner (3GPP), a simple feedback method based on codebook is adopted in the uplink channel information feedback in the LTE Release 8 (R8).
Generally, in the MIMO, the codebook feedback method is:
 A UE obtains the channel matrix information, and selects from the codebook a “Rank” value (which can also be interpreted as the number of layers for space multiplexing) mostly suitable to the current channel and a certain corresponding codeword PMI under this Rank. It is assumed that the base station uses MIMO, pre-codes according to the codeword, and calculates the corresponding CQI;
 the UE feeds back and recommends the calculated optimal RI/PMI/CQI on the uplink channel.
Wherein:
Rank Information (RI) represents the Rank information of the channel;
precoding Matrix Indicator (PMI) is precoding indicator information based o the codebook;
and Channel Quality Indicator (CQI) is channel quality indicator information after precoding, and can be interpreted as, but not completely equivalent to, the characterizing eigenvalue information to a certain extent. It is associated with the feedback precision of the PMI, and is generally represented quantitatively in the modulation coding mode of transmission blocks.
In the LTE standard 36-213 protocol, the CQI is indicated by integer values of 0-15, which represent different CQI levels respectively. Different CQIs correspond to respective modulation modes and coding code rates (i.e., Modulation Coding Scheme (MCS)), including 16 cases in total, and can be indicated using 4-bit information, as shown in Table 3, but is not limited to this CQI representing method.
TABLE 3Relationship between CQI index and MCSModulationCQI indexmodeCode rate x 1024Efficiency0Exceed1QPSK780.15232QPSK1200.23443QPSK1930.37704QPSK3080.60165QPSK4490.87706QPSK6021.1758716QAM3781.4766816QAM4901.9141916QAM6162.40631064QAM4662.73051164QAM5673.32231264QAM6663.90231364QAM7724.52341464QAM8735.11521564QAM9485.5547
In the MIMO system, the Rank is restraint to be 1 for feedback, and the vectors can only be quantified by selecting codewords from the codebook of Rank 1, the Rank information is defaulted and does not need to be fed back, and the CQI feedback method is similar to the traditional MIMO feedback method.
In the LTE-Advance (LTE-A), the performance of MIMO needs to be enhanced greatly in this version. If the feedback method in the original LTE MIMO mode is used, when it needs to dynamically switch to the Multiple User-MIMO (MU-MIMO) mode in the case of high Rank, since the higher Rank is, the lower the corresponding codebook precision is, the base station cannot obtain accurate channel feedback information to perform Interference suppression/cancellation in the precoding, and the precoding performance of the MU-MIMO will be very bad. However, if the feedback method of the MU-MIMO mode is used, the number of quantified vectors is too small, and cannot support the MIMO of high Rank.
Prior art 1: in the 802.16m standard, the adopted method is as follows: the RI/PMI/CQI is fed back according to the Single User-MIMO (SU-MIMO) mode. If it is high-Rank feedback, the first column is used, and the precoding is calculated using the function F to perform MIMO; or, all the columns are used, information of the user is based, and precoding is calculated using the precoding algorithm to perform MIMO. It is found through simulation that since few bits are used to quantify multiple vectors in the case of high Rank, the accuracy is very poor, and thus the performance is very bad.
Prior art 2: referring to FIG. 1, a terminal feeds back RI/PMI/CQI according to the SU-MIMO mode, and uses the enhanced technique, such as differential codebook and adaptive codebook, to improve the codebook precision. For example, RI/PMI/CQI is fed back according to the SU-MIMO mode, and it is assumed that PMI is W, and a codeword D is selected from the differential codebook Cdf and its corresponding index is fed back, and a rule Ω(W,D) is regulated, thus obtaining a more accurate vector feedback information. However, when feedback occurs in high Rank, i.e., there are multiple Ranks, as can be seen from FIG. 1, the Cdf in this solution needs to design a set of codewords for different Ranks of User Equipments (UEs), and it still need many codewords to adjust the W to be accurate enough.
Prior art 3: referring to FIG. 2, a terminal feeds back RI/PMI/CQI respectively according to different MIMO modes. The performance of this feedback is better than those of the previous two, but its feedback overhead is also the highest. As can be seen, two sets of feedback that are totally independent from each other are needed to feed back different MIMO systems in this solution.